Experimental study of temperature distributions and thermal transport during radiofrequency current therapy of the intervertebral disc.

Abstract

The authors measured the temperature changes within the human intervertebral disc during transient intradisc heating with a radiofrequency current lesion generator. The study was undertaken to evaluate the efficacy of thermal denervation of the intervertebral disc from intradisc radiofrequency lesion treatment. Intradisc radiofrequency heating has emerged recently as a nonoperative treatment for chronic lower back pain. However, no literature exists regarding the temperature distributions within the disc and the consequent efficacy of denervation. Vertebral segments obtained at autopsy were instrumented with thermocouples, and intradisc heating was performed according to standard clinical protocols. The tip was maintained at 70 C and the temperature monitored at various distances from the tip. The temperature changes at distances further than 11 mm were insufficient to raise the tissue temperature to the 42 C needed for neuronal cell death. Using the thermal transient data, the authors calculated the thermal diffusivity of the human intervertebral disc and found it to vary from approximately 1.7 x 10(-7) +/- 0.4 x 10(-7) m2/sec in the disc from a 61-year-old man to approximately 4.5 x 10(-7) +/- 1.4 x 10(-7) m2/sec in the disc from a 32-year-old man. The authors concluded that the mechanism of observed clinical improvement from radiofrequency heating of intervertebral discs is not thermal denervation of the disc and that the physicochemical state of the disc is important to consider when designing a therapeutic heating protocol if thermal denervation is clinically desired.